Topband: 259B

[Paul Higginson]

In message <006201c42094$69d93df0$0c887ad5 at usero2cu908sdx>, Clive GM3POI 
<gm3poi2 at btinternet.com> writes
>Has any one come across the problem of a 259B showing on switch on
>0.000mhz for frequency and is the same on all bands. Is there any form of
>master reset that I can try?. 73 Clive GM3POI

I haven't seen a reply via the group so here goes....

Usually the reason for the display not reading ANY frequency is that 
there isn't one to read. ( confirm the unit still works as a counter by 
sniffing a bit of RF into the counter input )

There are several causes, the diagrams and calibration guide is 
available on the net.

http://www.cqham.ru/ftp2/mfj259-cal.pdf

A quick google will find the schematic, if you can't find it, let me 
know I'll email a copy of mine.

If you are correct and the display reads zero at ALL settings of the 
bandswitch and variable capacitor setting the oscillator has most likely 
failed.

Usually when it's a catastrophic failure it's caused by a couple of 
things.

The small voltage regulator damaged by supply spike

the final amplifier fails as a result of reverse polarity from an 
external power source but the symptoms are slightly different ( erratic 
reading of frequency and VSWR reading drastically inaccurate )

I do have one here with a faulty smt osc transistor, which is IME 
uncommon.

If you haven't checked, or you missed the following clue, you might find 
that the oscillator runs at some frequencies but not others ( hence 
reads 00000 at certain dial settings )

This is often due to damage or contamination between the capacitor 
plates.

If no one has randomly twiddled... this is NEVER due to misalignment. 
Fix the fault, don't twiddle the cores / pots till it's working.

Follow the calibration procedure carefully and use good quality 
resistors and phasing lines to set it up and it will be a doddle.

Regards
-- 
73 de Paul GW8IZR IO73TI        |If you are not the intended recipient of this
http://www.gw8izr.com           | email - it probably makes no sense at all!

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